This invention relates to collecting and absorbing high concentrations of solar energy for heating a working fluid and more particularly to a concentrating solar collector having dual axis sun tracking apparatus controllably driven to obtain optimum focus of the sun's radiation and driven into a stow position when darkness or certain weather conditions prevail.
Although many attempts have been made in the prior art to collect and concentrate the electromagnetic waves of the solar spectrum and to utilize the energy for thermal applications, the known systems have not proven to be economically feasible. To concentrate and recover the large amounts of energy required for most practical applications it is necessary to provide collectors having reflective surfaces in the order of at least 30 feet. The structural requirements of such large units present weight and cost programs that have not yielded ready solutions. In Brantley U.S. Pat. No. 4,033,676 a deformable bag enclosure is carried between a pair of spaced hoop members connected together by a number of struts and a reflective surface coextensive with the upper hoop deforms to the desired configuration when a partial vacuum is drawn between the reflective surface and the enclosure. This construction, although providing an inexpensive light weight collector apparatus, is limited to small size applications because of the structural stability of the unit and since the depth of the reflector is substantial relative to the diameter. Moreover, because there is no rear backing structure, a collector of that construction cannot be utilized in applications where rear mounted structure is required as, for example, where azimuth/elevation tracking drives are utilized.
Another limitation of the known prior art solar collector systems is the absorber which traps the reflected energy for heating the working fluid. Most of the known prior art solar energy absorbers or traps are of the transparent cover type units which have a high degree of radiation and convective loss. In Brantley U.S. Pat. No. 3,958,553 an absorber having a light pipe configuration is disclosed which works quite well for high temperature application in the range of 500.degree. to 1000.degree. F. It however utilizes a fluid flowing down the side walls to cool the walls to create a temperature gradient from the mouth to the high temperature section, and requires a relatively large length to diameter ratio.
For lower temperature applications an anti-radiating absorber having a honeycomb structure is more economically feasible. This type of absorber comprises a bundle of parallel very small diameter glass tubes within a cylindrical body, the cylinder having an inner surface of low absorptivity and high emissivity, and the tubes being transparent to solar rays and a high emissivity to thermic rays. Incoming solar radiation passes partly through the walls of the tubes and is partly reflected to the boiler which is perpendicular to the tube axes. The reradiation from the hot boiler is absorbed by the walls of the tubes, which upon heating radiates energy in all directions and the boiler recovers a portion of this energy. However, the known absorbers using this principle have in the past been of complicated configurations and economically unfeasible for practical applications. In the known absorbers the tubes were of long lengths and had extremely small diameters. The tubes were banded together and held in place by an annular-ring member.
Further limitations of the known prior art collectors are their inability to acurately trace and follow the sun, thereby resulting in failure of the reflector to optimumly focus the rays on the absorber with resultant loss of efficiency. Moreover, the known prior systems must be activated daily and manually shut down when solar insolation is limited and when weather conditions are critical.